1. Field Of the Invention
This invention is directed to solid electrolytes containing a polymer matrix and a novel electrolyte salt. The novel electrolyte salt has an anion portion which functions as a counter ion to a metal ion. The novel electrolyte salt can partially or completely replace the inorganic ion salt and/or electrolytic solvent used in conventional solid electrolytes.
2. State of the Art
Electrolytic cells containing an anode, a cathode and a solid, solvent-containing electrolyte are known in the art and are usually referred to as "solid batteries." See, instance, U.S. Pat. Nos. 5,229,225, 5,238,758, 5,358,801, and 5,366,829. These cells offer a number of advantages over electrolytic cells containing a liquid electrolyte (i.e., "liquid batteries") including improved safety features.
For electrolytic cells, the inorganic ion salts typically have a transference number between 0.4 and 0.55, meaning that the ion salt carries only between 40% and 55% of the total plus (+) charge. The relatively low transference number also adversely affects cumulative capacity. The cumulative capacity of a solid battery is defined as the summation of the capacity of the battery over each cycle (charge and discharge) in a specified cycle life.
Another problem with current electrochemical cells relates to solvent volatility. In a typical solid electrolytic cell, the solid electrolyte contains a solvent (plasticizer) which is added to the polymeric matrix primarily to enhance the solubility of the inorganic ion salt in the solid electrolyte and thereby increase the conductivity of the electrolytic cell. Unfortunately, a significant quantity of solvent evaporates during processing to form the solid electrolyte. To retain sufficient solvent in the final product therefore requires a higher initial amount of solvent in the electrolyte formulation. This increases both raw material and processing costs since the evaporated solvent must either be recaptured, recycled or disposed of.
In view of the above, the art is searching for methods to improve the conductivity of solid electrolytes and the cumulative capacity of solid batteries employing such solid electrolytes. Furthermore, there is a need in the art for reducing or eliminating problems associated with solvent volatility.